The present invention relates to a gas generating material. The gas generating material is particularly useful for inflating a vehicle occupant protection device.
An inflatable vehicle occupant protection device, such as an air bag, is inflated by gas provided by an inflator. The inflator contains a gas generating material. The inflator further includes an igniter. The igniter is actuated to ignite the gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
A convenient way of making a gas generating material is by extrusion. Gas generating material that is extruded can be configured into a variety of structural shapes, including rods, pellets, and other shapes. Conventional extrusion of gas generating material requires formulating the gas generating material with a thermoplastic elastomer binder. Thermoplastic elastomer binders conventionally have a low oxygen content. This requires formulating the gas generating material with a relatively large amount of an oxidizer to oxygen balance the gas generating material and produce a combustion product which is substantially smoke-free and substantially free of toxic materials. The use of a large amount of oxidizer, however, makes extrusion processing difficult.
Moreover, it is desirable to recycle gas generating material that has not been ignited. This avoids disposing the gas generating material in a land fill. However, conventional thermoplastic elastomer binders in gas generating material are cross-linked by chemical bonds such as covalent bonds. Covalent bonds are difficult to break, thus making it difficult to convert the gas generating material to its original ingredients for recycling.
The present invention is an apparatus comprising an inflatable vehicle occupant protection device and a gas generating material that, when ignited, produces gas to inflate the inflatable vehicle occupant protection device. The gas generating material comprises a polyurethane thermoplastic elastomer and an inorganic salt oxidizer. The polyurethane elastomeric material comprises a physically cross-linked linear copolymer of an aromatic diisocyanate and a linear energetic polymer having a hydroxyl functionality of two or less.